A related-art control device configured to lower an inverter bus voltage to drive a motor includes: a converter connected to a DC power supply and configured to boost output of the DC power supply for output to an inverter; the inverter configured to convert the output of the converter into AC power for output to a rotary electric machine; and a control unit configured to control the inverter and the converter. The control device switches from PWM control to rectangular wave control when a temperature detection unit configured to detect temperature of a switching element has detected that the temperature of the switching element has reached a predetermined temperature (refer to Patent Literature 1, for example).
Further, another related-art control device configured to lower an inverter bus voltage to drive a motor includes: a DC/DC converter connected to a battery; an inverter; a control unit configured to control the inverter; and a motor generator (rotary electric machine having both functions of a motor configured to be driven through application of a voltage by the inverter and a generator configured to generate electric power by its shaft being driven by an external force). The control unit executes a method involving lowering an input voltage of the inverter and switching a control mode of the inverter from a sinusoidal PWM control mode to an over-modulation control mode or a rectangular wave control mode when a driving frequency at the time of sinusoidal PWM control matches a frequency in a resonance frequency region of an LC resonance circuit (refer to Patent Literature 2, for example).